Method and Apparatus for Accurate, Digital Monitoring a Receiver Frequency via Telemetry without the Need for Calibration of Analog Components
The novel feature of this invention is that it uses digital hardware that is added to the receiver for the specific purpose of monitoring the frequency and then it produces a calibrated value of the receiver frequency. Present methods for monitoring the frequency of a phase-locked receiver require calibration that can be invalidated by aging, temperature changes, or other physical effects. The APL approach is not subject to variations in analog components, other than the frequency reference.
This APL invention is the use of a small amount of additional hardware to a spacecraft communications receiver for the purpose of continuous monitoring of the receiver frequency. This invention could be immediately included in any new transponder or transceiver designs. It requires only the addition of two counters with some associated logic and a means for obtaining occasional samples of those counters. A simple calculation based on those samples accurately indicates the receiver frequency in either the locked or unlocked states. The information obtained from the calculation based on samples of these added counters can be used to save time in the process of creating a command/control uplink to the spacecraft by providing the ground controller accurate knowledge of the changes in the receiver characteristics over time. It allows more rapid characterization of the receiver during acceptance testing. During flight, the ground controllers can use the current known state of the receiver, rather than a “worst case” understanding, to design an efficient uplink acquisition approach. This invention has been successfully demonstrated on the TIMED and CONTOUR missions. The new application includes: · Using the telemetered counter values to compute the "best lock frequency" of the receiver when no input signal is present. This allows the user to determine what input signal frequency will place the least stress on the receiver tracking capability and it allows the user to quickly establish receiver lock by choosing an efficient frequency sweep strategy. This will improve the use of costly ground station time. · Using the telemetered counter values to compute the receiver input frequency when an input signal is present. This allows the user to verify that the input signal frequency is maintained at a desired point in the presence of Doppler shifts and may be used to make a rough estimate of the Doppler velocity without the use of a ground-based Doppler measurement. · Combining the counter values with a measurement of a phase-locked loop static phase error to monitor variations in the best lock frequency over time. This will allow the user to maintain the receiver input near the best lock frequency and to know what input frequency will quickly lock up the receiver if the link is broken and must be re-established. · Acceptance and preflight characterization of a receiver where the receiver frequency can be continuously monitored over time and temperature. This eliminates the conventional need to repeatedly sweep the input frequency to determine the best lock frequency. Each sweep must be followed by a long relaxation time which increases the time and cost of testing and characterizing a receiver. · In-flight diagnosis of acquisition problems. The complete acquisition process can be watched and any failures to achieve or hold receiver lock can be recognized and remedied.
Patent Status: U.S. patent(s) 7206575 issued.
*This JHU/APL invention is available for licensing.CONTACT:
Mr. J. E. Dietz
Phone: (443) 778-2782